All steel, no welding, 2000x1300x250mm

[routercnc]

I've just jumped into this thread and I would think twice about welding the rails. They will almost certainly bend out of alignment with the heat and shrinkage, even I suspect with TIG which can be more delicate.

It may also remove the hardening from the local area although that will probably be the least of your problems.

Don't want to knock your ideas but I would seriously check whether this is a good strategy - so buy a very small length of rail, put a bearing on it with a cheap laser pointer aimed a a wall. Mark the spot, then weld the rail to a something to replicate the support post and see what happens to the spot. Then decide if this approach is going to work before spending money on all the laser cutting . . .

To be honest, supported round rail would be a much better option and it is easy to bolt down via the flanges.